Stretch Band Research Articles

Amorphous Solid Water (ASW): Pulsed Laser Ablation of ASW/CO2 Thin Films

Thin films composed of 400–500 monolayers (ML) of either amorphous solid water (ASW) or ASW/CO2 mixtures are grown atop a MgO(100) substrate under ultrahigh vacuum conditions. Samples are irradiated at an infrared frequency of 3424 cm–1, which lies within the broad OH stretch band of condensed water. Ablation is achieved using 10 ns pulses whose energy (<2.7 mJ) is focused to a beam waist of approximately 0.5 mm. By using a time-of-flight mass spectrometer to monitor ablated material, excellent single-shot detection is demonstrated. This capability is essential because, in general, the first infrared pulse can induce irreversible changes throughout the irradiated volume. With ASW/CO2 samples, CO2 is released preferentially. This is not surprising in light of the metastability of the samples. Indeed, repeated irradiation of the same spot can rid the sample of essentially all of the CO2 in as little as a few pulses, whereas only 10–20 ML of H2O are removed per pulse. The influence of the substrate is profou...

High Resolution IR Spectroscopy of the C–H Stretch Bands of Benzene Monomer and Dimer in Helium Nanodroplets

Abstract The IR spectrum of benzene and benzene dimer embedded in superfluid helium droplets in the region of the C–H stretch vibration (3000–3110 cm-1) was observed. By analyzing the pressure dependence of the spectra it was possible to assign these spectra to benzene monomer and dimer. Based on a comparison of the observed position of the dimer bands to experimental bands recorded in the gas phase and to theoretical frequency predictions the authors assign these to the tilted T-shaped benzene dimer structure. None of the other two possible structures (PD or PTS) were found. The above assignment is firm. For the monomer, we find in helium nanodroplets a splitting of the ν 8+ν 19 combination band observed in the gas phase. We assign this to an additional Fermi resonance which is caused by the matrix shift in helium nanodroplets.

The Importance of Protonation in the Investigation of Protein Phosphorylation Using Raman Spectroscopy and Raman Optical Activity

The effect of protonation on amino acid monomers and protein phosphorylation was studied by means of a combination of Raman scattering and Raman optical activity (ROA). In the past, identifying spectral variations in phosphorylated proteins arising from either the phosphate stretch or amide vibrational modes has proven to be challenging mainly due to the loss of amide and P═O band intensity in the presence of phosphate. By contrast, we have developed a novel strategy based on the careful monitoring of the sample pH and thereby modified the protonation state, such that these difficulties can be overcome and phosphate-derived vibrations are readily visualized with both Raman and ROA. Variations in pH-dependent spectral sets of phosphorylated amino acid monomers serine and threonine demonstrated that the protonation state could be determined by the intensity of the monobasic (-OPO(3)H(-)) phosphate stretch band occurring at ~1080 cm(-1) versus the dibasic (-OPO(3)(2-)) band measured at ~980 cm(-1) in both Raman and ROA. Furthermore, by adjustment of the pH of aqueous samples of the phosphoprotein α-casein and comparing this result with dephosphorylated α-casein, spectral variations in phosphate stretch bands and amide bands could be easily determined. Consequently, structural variations due to both protonation and dephosphorylation could be distinguished, demonstrating the potential of Raman and ROA for future investigations of phosphoprotein structure and interactions.

Study on the Structure and Spectrum of Water in 1-Ethyl-3-Methylimidazolium Tetrafluoroborate Ionic Liquids

Various 1-ethyl-3-methylimidazolium tetrafluoroborate ([Emim]BF4)/water mixture with varying concentrations were studied by molecular dynamics simulations. The radial distribution function, the power spectrum velocity-velocity correlation function were calculated to reveal the microstructure and the IR spectrum. In both liquids, with the concentration of water in the mixture increase, the rotation bands and the bending bands of water are red shift whereas the O-H stretch bands are blue shift. It was found that the molecular rotation motions become slower as the proportion of water increases and water molecules tend to be isolated from each other in mixtures with more ions than water molecules. It was shown that water molecules tend to be isolated from each other in mixtures with more ions than water molecules in both liquids.

Solvation-Induced σ-Complex Structure Formation in the Gas Phase: A Revisit to the Infrared Spectroscopy of [C6H6–(CH3OH)2]+

Structures of the [C(6)H(6)-(CH(3)OH)(2)](+) cluster cation are investigated with infrared (IR) spectroscopy. While the noncovalent type structure has been confirmed for the n = 1 cluster of [C(6)H(6)-(CH(3)OH)(n)](+), only contradictory interpretations have been given for the spectra of n = 2, in which significant changes have been observed with the Ar tagging. In the present study, we revisit IR spectroscopy of the n = 2 cluster from the viewpoint of the σ-complex structure, which includes a covalent bond formation between the benzene and methanol moieties. The observed spectral range is extended to the lower-frequency region, and the spectrum is measured with and without Ar and N(2) tagging. A strongly hydrogen-bonded OH stretch band, which is characteristic to the σ-complex structure, is newly found with the tagging. The remarkable spectral changes with the tagging are interpreted by the competition between the σ-complex and noncovalent complex structures in the [C(6)H(6)-(CH(3)OH)(2)](+) system. This result shows that the microsolvation only with one methanol molecule can induce the σ-complex structure formation.

Quantum Cascade Laser Spectroscopy and Photoinduced Chemistry of Al–(CO)n Clusters in Helium Nanodroplets

Helium nanodroplet isolation and a tunable quantum cascade laser are used to probe the fundamental CO stretch bands of aluminum carbonyl complexes, Al-(CO)(n) (n ≤ 5). The droplets are doped with single aluminum atoms via the resistive heating of an aluminum wetted tantalum wire. The downstream sequential pick-up of CO molecules leads to the rapid formation and cooling of Al-(CO)(n) clusters within the droplets. Near 1900 cm(-1), rotational fine structure is resolved in bands that are assigned to the CO stretch of a linear (2)Π(1/2) Al-CO species and the asymmetric and symmetric CO stretch vibrations of a planar C(2v) Al-(CO)(2) complex in a (2)B(1) electronic state. Bands corresponding to clusters with n ≥ 3 lack resolved rotational fine structure; nevertheless, the small frequency shifts from the n = 2 bands indicate that these clusters consist of an Al-(CO)(2) core with additional CO molecules attached via van der Waals interactions. A second n = 2 band is observed near the CO stretch of Al-CO, indicating a local minimum on the n = 2 potential consisting of an "unreacted" (Al-CO)-CO cluster. The line width of this band is ∼0.3 cm(-1), which is about 30 times broader than the transitions within the Al-CO band. The additional broadening is consistent with a homogeneous mechanism corresponding to a rapid vibrational excitation induced reaction within the (Al-CO)-CO cluster to form the covalently bonded Al-(CO)(2) complex. Ab initio CCSD(T) calculations and natural bond orbital (NBO) analyses are carried out to investigate the nature of the bonding in the n = 1, 2 complexes. The NBO calculations show that both π-donation (from the occupied aluminum p orbital into a π* antibonding CO orbital) and σ-donation (from CO into the empty aluminum p orbitals) play a significant role in the bonding, analogous to transition-metal carbonyl complexes. The large red shift observed for the CO stretch vibrations is consistent with this bonding analysis.

Rotationally resolved infrared spectrum of the Na+-D2 complex: An experimental and theoretical study

The infrared spectrum of mass-selected Na(+)-D(2) complexes is recorded in the D-D stretch vibration region (2915-2972 cm(-1)) by detecting Na(+) photofragments resulting from photo-excitation of the complexes. Analysis of the rotationally resolved spectrum confirms a T-shaped equilibrium geometry for the complex and a vibrationally averaged intermolecular bond length of 2.461 Å. The D-D stretch band centre occurs at 2944.04 cm(-1), representing a -49.6 cm(-1) shift from the Q(1)(0) transition of the free D(2) molecule. Variational rovibrational energy level calculations are performed for Na(+)-D(2) utilising an ab initio potential energy surface developed previously for investigating the Na(+)-H(2) complex [B. L. J. Poad et al., J. Chem. Phys. 129, 184306 (2008)]. The theoretical approach predicts a dissociation energy for Na(+)-D(2) of 923 cm(-1) with respect to the Na(+)+ D(2) limit, reproduces the experimental rotational constants to within 1-2%, and gives a simulated spectrum closely matching the experimental infrared spectrum.

Spectra and Integrated Band Intensities of the Low Order OH Stretching Overtones in Peroxyformic Acid: An Atmospheric Molecule with Prototypical Intramolecular Hydrogen Bonding

The gas phase spectra of several vibrational bands of peroxyformic acid (PFA), an atmospheric molecule exhibiting intramolecular hydrogen bonding, are presented. In the fundamental region, Fourier transform infrared (FT-IR) spectroscopy is used to probe the C-O, O-H and C-H stretching vibrations, while in the region of the first and second OH-stretching overtones (2ν(OH) and 3ν(OH)) photoacoustic spectroscopy is used. Integrated absorption cross sections for the PFA vibrational bands are determined by comparing their respective peak areas with that for the OH-stretching bands of n-propanol for which the absorption cross section is known. The measured integrated intensities of the OH stretching bands are then compared with a local mode model using a one-dimensional dipole moment function in conjunction with the OH stretching potential computed at both the MP2/aug-cc-pVDZ and CCSD(T)/aug-cc-pVDZ levels. The data allow us to investigate changes in the OH stretch band position and intensity as a function of overtone order arising from the influence of hydrogen bonding. Furthermore, calculations at the MP2/aug-cc-pVDZ level show that there are three stable conformers of PFA with relative energies of 0, 13.54, and 13.76 kJ/mol, respectively. In the room temperature spectra, however, we see evidence for transitions from only the lowest energy conformer. The geometrical parameters and vibrational frequencies of the most stable conformer are presented.

Isotope effects in liquid water by infrared spectroscopy. V. A sea of OH4 of C2v symmetry

The two water gas OH stretch vibrations that absorb in the infrared (IR) near 3700 cm(-1) are redshifted to near 3300 cm(-1) upon liquefaction. The bathochromic shift is due to the formation of four H-bonds: two are from the labile hydrogen atoms to neighbors and two are received from neighbors by the oxygen free electron pairs. Therefore, the water oxygen atom is surrounded by four hydrogen atoms, two of these make covalent bonds that make H-bonds and two are oxygen H-bonded. However, these permute at rate in the ps range. When the water molecules are isolated in acetonitrile (MeCN) or acetone (Me(2)CO), only the labile hydrogen atoms make H-bonds with the solvent. The bathochromic shift of the OH stretch bands is then almost 130 cm(-1) with, however, the asymmetric (ν(3)) and symmetric (ν(1)) stretch bands maintained. When more water is added to the solutions, the oxygen lone doublets make H-bonds with the available labile hydrogen atoms from neighboring water molecules. With one bond accepted, the bathochromic shift is further displaced by almost 170 cm(-1). When the second oxygen doublet is filled, another bathochromic shift by almost 100 cm(-1) is observed. The total bathochromic shift is near 400 cm(-1) with a full width at half height of near 400 cm(1). This is the case of pure liquid water. Notwithstanding the shift and the band broadness, the ν(3) and ν(1) band individualities are maintained with, however, added satellite companions that come from the far IR (FIR) absorption. These added to the fundamental bands are responsible for the band broadness and almost featureless shape of the massive OH stretch absorption of liquid water. Comparison of light and heavy water mixture spectra indicates that the OH and OD stretch regions show five different configurations: OH(4); OH(3)D; OH(2)D(2); OHD(3); and OD(4) [J. Chem. Phys. 116, 4626 (2002)]. The comparison of the OH bands of OH(4) with that of OHD(3) indicates that the main component in OHD(3) is ν(OH), whereas in OH(4) two main components are present: ν(3) and ν(1). Similar results are obtained for the OD bands of OD(4) and ODH(3). These results indicate that the C(2) (v) symmetry of H(2)O and D(2)O is preserved in the liquid and aqueous solutions whereas C(s) is that of HDO.

Spin state transitions upon visible and infrared excitation of ferric MbN3

When azide binds to ferric Myoglobin it forms either a low-spin or a high-spin complex, which give rise to two well-separated asymmetric stretch bands of the ligand. Both electronic excitation of the Q-band and vibrational excitation of N3- in the mid-IR lead to a similar ultrafast population redistribution in favor of the high spin configuration, which is characterized by a 8° reorientation of the ligand transition dipole moment. The more stable low spin complex subsequently re-emerges with a 18ps time-constant. It is argued that the observed spin state changes are caused by the participation of low-lying electronic excitations in the cooling process of heme.

Structural and Electric Field Effects of Ions in Aqueous Nanodrops

Ensemble infrared photodissociation (IRPD) spectra in the hydrogen stretch region (∼2950-3800 cm(-1)) are reported for M(H(2)O)(35-37), with M = I(-), Cl(-), HCO(3)(-), OH(-), tetrabutyl-, tetrapropyl-, and tetramethylammonium, Cs(+), Na(+), Li(+), H(+), Ba(2+), Ca(2+), Co(2+), Mg(2+), La(3+), and Tm(3+), at 133 K. A single, broad feature is observed in the bonded-OH region of the spectra that indicates that the water network in these clusters is bulk-like and likely resembles liquid water more strongly than ice. The free-OH region for all of these clusters is dominated by peaks corresponding to water molecules that accept two and donate one hydrogen bond (AAD water molecules), indicating that AAD water molecules are more abundant at the surface of these ions than AD water molecules. A-only water molecules are present in significant abundance only for the trivalent metal cations. The frequency of the AAD free-OH stretch band shifts nearly linearly with the charge state of the ion, consistent with a Stark shift attributable to the ion's electric field. From these data, a frequency range of 3704.9-3709.7 cm(-1) is extrapolated for the free-OH of AAD water molecules at the (uncharged) bulk liquid water surface, consistent with sum-frequency generation spectroscopy experiments. Differences in both the bonded- and the free-OH regions of the spectra for these ions are attributable to ion-induced patterning of the water network that extends to the surface of the clusters, which includes water molecules in the third and fourth solvation shells; that is, these ions pattern water molecules at long distance to various extents. These spectra are simulated using two different electrostatic models previously used to calculate OH-stretch spectra of bulk water and aqueous solutions and parametrized for bonded-OH frequencies. These models qualitatively reproduce a number of features in the experimental spectra, although it is evident that more sophisticated treatment of water molecule and ion polarizability and vibrational coupling is necessary for more quantitative comparisons.

Structural trends of ionized water networks: Infrared spectroscopy of watercluster radical cations (H2O)n+ (n = 3–11)

The nature of water networks exposed to ionizing radiation is important in various radiation-related chemistry and biology. To understand structural evolution of ionized water networks at the molecular level, we report here infrared spectra of watercluster radical cations (H2O)n+ (n = 3 − 11) in the gas phase. Spectral features of free OH stretch modes are quite similar to those of protonated waterclustersH+(H2O)n, of which the hydrogen-bond network structures have been revealed. In addition, we observed an extra band attributed to the stretch of an OH radical in (H2O)n+. These results indicate that nominal (H2O)n+ should be regarded as H+(H2O)n−1(OH) motifs having similar network shapes to those of H+(H2O)n. We also analyzed hydrogen-bonded OH stretch bands and found that hydrogen-bond strength is a key factor to determine the position of the OH radical relative to the protonated site (H3O+/H5O2+). Because an OH radical is a weaker hydrogen bond acceptor than water, the first solvation shell of the protonated site is preferentially filled with water. As a result, the OH radical is separated from the protonated (charged) site by at least one water molecule in n ≥ 5 clusters. This result shows the instability of the H3O+-OH ion-radical contact pair in water networks, and implies the higher mobility of the OH radical due to its release from the charged site. Observed structural preferences are confirmed both in cold and warm clusterion sources.

Temperature of mesospheric ice particles simultaneously retrieved from 850 cm−1libration and 3200 cm−1vibration band spectra measured by ACE-FTS

[1] We report a new approach to the retrieval of ice particle temperature in the atmosphere from midinfrared remote sensing observations. Two different in physical nature spectral bands of water ice, the libration band near 850 cm−1 and O-H stretch band at 3200 cm−1, are used simultaneously. The use of both bands in the unified least squares fitting procedure enables one to enhance the stability of fitting, as well as to improve the reliability and accuracy of retrieved ice temperature values. A set of reference spectra for the least squares minimization is compiled from experimental temperature-dependent optical constants for water ice that are available in the literature. The method is applied to the observations made by the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) instrument on board the SCISAT-1 satellite. According to our results, a combination of the vibration (3200 cm−1) and rotation (850 cm−1) bands within a unified minimization procedure can significantly, by about 4K, reduce the upper estimate of the total uncertainty in the retrieved temperatures from 12 K down to 8 K. The average temperature of bright mesospheric ice clouds observed by ACE-FTS during July 2005 is found to be about 131K, in contrast to the value of 135K retrieved from the vibration band alone.

Infrared Spectra of the Azide Asymmetric Stretching Band in a Model Compound, a Peptide Containing Beta-Azido Alanine, and in Carbohydrates

Infrared spectra of the model compound 5-azido,1-pentanoic acid were used to characterize the behavior of the asymmetric azide stretching peak in different solvents. The frequency and width of the peak changed depending on the solvent. The greatest change was seen between all non-aqueous azide bands and the band in water, which was blue shifted substantially from the nonaqueous peaks. Spectra were collected in mixed water/organic solvent solutions, sugar/water solutions, and under changing temperatures to determine the behavior of the azide peak. A model alanine-repeat peptide with an azide-labeled amino acid was synthesized, and temperature-dependent IR experiments of the aqueous peptide were used to assess the sensitivity of the azide peak to peptide folding. The possible application of site specific azide labeled carbohydrates has also been explored.

Potential energy surface and rovibrational calculations for the ${\rm Mg}^+$ Mg +–${\rm H}_2$H2 and ${\rm Mg}^+$ Mg +–${\rm D}_2$D2 complexes

A three-dimensional potential energy surface is developed to describe the structure and dynamical behavior of the Mg(+)-H(2) and Mg(+)-D(2) complexes. Ab initio points calculated using the RCCSD(T) method and aug-cc-pVQZ basis set (augmented by bond functions) are fitted using a reproducing kernel Hilbert space method [Ho and Rabitz, J. Chem. Phys. 104, 2584 (1996)] to generate an analytical representation of the potential energy surface. The calculations confirm that Mg(+)-H(2) and Mg(+)-D(2) essentially consist of a Mg(+) atomic cation attached, respectively, to a moderately perturbed H(2) or D(2) molecule in a T-shaped configuration with an intermolecular separation of 2.62 Å and a well depth of D(e) = 842 cm(-1). The barrier for internal rotation through the linear configuration is 689 cm(-1). Interaction with the Mg(+) ion is predicted to increase the H(2) molecule's bond-length by 0.008 Å. Variational rovibrational energy level calculations using the new potential energy surface predict a dissociation energy of 614 cm(-1) for Mg(+)-H(2) and 716 cm(-1) for Mg(+)-D(2). The H-H and D-D stretch band centers are predicted to occur at 4059.4 and 2929.2 cm(-1), respectively, overestimating measured values by 3.9 and 2.6 cm(-1). For Mg(+)-H(2) and Mg(+)-D(2), the experimental B and C rotational constants exceed the calculated values by ∼1.3%, suggesting that the calculated potential energy surface slightly overestimates the intermolecular separation. An ab initio dipole moment function is used to simulate the infrared spectra of both complexes.

Infrared spectroscopy of Sc+(H2O) and Sc2+(H2O) via argon complex predissociation: The charge dependence of cation hydration

Singly and doubly charged scandium-water ion-molecule complexes are produced in a supersonic molecular beam by laser vaporization. These ions are mass analyzed and size selected in a specially designed reflectron time-of-flight spectrometer. To probe their structure, vibrational spectroscopy is measured for these complexes in the O-H stretching region using infrared laser photodissociation and the method of rare gas atom predissociation, also known as "tagging." The O-H stretches in these systems are shifted to lower frequency than those for the free water molecule, and the intensity of the symmetric stretch band is strongly enhanced relative to the asymmetric stretch. These effects are more prominent for the doubly charged ions. Partially resolved rotational structure for the Sc(+)(H(2)O)Ar complex shows that the H-O-H bond angle is larger than it is in the free water molecule. Fragmentation and spectral patterns indicate that the coordination of the Sc(2+) ion is filled with six ligands (one water and five argons).

Photoionization-induced large-amplitude pendular motion in phenol+–Kr

The dynamics of the intermolecular motion of the phenol(+)-Kr cation generated by photoionization of the neutral π-structure is probed by picosecond time-resolved infrared spectroscopy. The spectrum at zero delay displays only the free OH stretch band of the π-structure. The appearance of the hydrogen-bonded OH stretch band of the H-structure after a few ps is due to ionization-induced π → H site switching. Spectra at long delay (>20 ns) show that the Kr atom delocalizes from one π-site of the aromatic ring to the opposite π-site via the OH-site, like a pendular motion in the classical picture.

The influence of juggling on mental rotation performance in children

The influence of juggling on mental rotation performance in children Study aim: To assess the influence of juggling training on mental rotation performance in children. Material and methods: Two groups of girls aged 6 - 14 years were studied: experimental (EG; n = 26) and control (CG; n = 24). All girls solved a mental rotation task with 3-D block figures on computer screen (pre-test). After the initial test, EG girls participated in juggling training for 3 months; the CG girls participated in light strength training with theraband stretch bands. After 3 months, all girls solved the mental rotation task again (post-test). The post-pre differences in the mental rotation performance were recorded. Results: Children who learned juggling performed the mental rotation task significantly (p&lt;0.05 - 0.01) faster, in terms of reaction time, at non-zero angular disparity than their mates who were strength-trained. Conclusions: Since mental rotation skills enhance spatial imagination, problem solving and mathematical skills, it may be assumed that juggling training enhances also other cognitive domains and is worth implementing in the education process.

Spectral Signatures of Four-Coordinated Sites in Water Clusters: Infrared Spectroscopy of Phenol−(H2O)n (∼20 ≤ n ≤ ∼50)

We report infrared spectra of phenol-(H(2)O)(n) (∼20 ≤ n ≤ ∼50) in the OH stretching vibrational region. Phenol-(H(2)O)(n) forms essentially the same hydrogen bond (H-bond) network as that of the neat water cluster, (H(2)O)(n+1). The phenyl group enables us to apply the scheme of infrared-ultraviolet double resonance spectroscopy combined with mass spectrometry, achieving the moderate size selectivity (0 ≤ Δn ≤ ∼6). The observed spectra show clear decrease of the free OH stretch band intensity relative to that of the H-bonded OH band with increasing cluster size n. This indicates increase of the relative weight of four-coordinated water sites, which have no free OH. Corresponding to the suppression of the free OH band, the absorption peak of the H-bonded OH stretch band rises at ∼3350 cm(-1). This spectral change is interpreted in terms of a signature of four-coordinated water sites in the clusters.

Palladium(II) and Platinum(II) Complexes of N-Phenyl- and N-Ethyl-N′-pyrimidin-2-ylthiourea

Palladium(II) and platinum(II) complexes of N-ethyl-N′-pyrimidin-2-ylthiourea(HL1) and N-phenyl-N′-pyrimidin-2-ylthiourea (HL2) have been prepared, and the complexes [M(HL)Cl2], [Pt(L)2], [Pd(HL1)2]Cl2, and [Pd(L2)2] (where M = PdII or PtII) were characterized. The spectroscopic data are consistent with coordination of thioureas as neutral or monoanionic ligands to PdII and PtII through S and a pyrimidine-N. The IR spectra show shifts of CS and pyrimidine ring stretch bands to lower and higher frequencies, respectively. The 1H NMR spectra differentiate between H(4′) and H(6′) resonances and indicate downfield shifts for all protons of pyrimidine [H(4′), H(5′), and H(6′)], two resonances for two N‒H protons for complexes containing the neutral ligand (HL), and only one N‒H proton chemical shift for complexes containing the monoanion (L). 13C NMR chemical shifts of pyrimidine carbons are correlated with the type of bonding between PdII or PtII and pyrimidine-N. The magnetic susceptibilities suggest a diamagnetic planar structure for all complexes. Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.